Radio receiving system



Feb. 8, 1938. K. SCHLESINGER RADIO RECEIVING SYSTEM Filed Nov. 21, 1934 7n venioc v Patented Feb. 8, 1938 PATENT orFic RADIO RECEIVING SYSTEM Kurt Schlesinger, Berlin, Germany Application November 21, 1934, Serial No. 754,049 In Germany November 24, 1933 6 Claims.

When incoming radio waves are mixed with locally generated oscillations two new frequencies are generated, the difference and the sum of the received frequency and the locally generated frequency. The one, the difference frequency is used in the superheterodyne-receiver.

The other one, the sum frequency is employed in the infradyne-receiver. In both the cases the tuning of the local oscillator is changed in such a way that a constant intermediate-frequency (the difference or the sum-frequency) is produced. After amplification this intermediate frequency is detected for selecting the signal frequencies, which are superposed on the incoming waves and therefore also on the intermediate frequency.

This invention relates to an infradyne receiver in which a high selectivity is effected by coupling the output circuit of the mixing device with the intermediate frequency amplifier by a piezo-electric circuit. According to the invention a defined relation between the intermediate frequency, the highest modulation frequency and the damping decrement of the pieZo-crystal shall be accomplished, in order to prevent suppressing of the external frequencies of the sideband of the modulated carrier by reason of the narrow resonant curve of the piezo-circuit.

According to the invention this defined relation can be effected by choosing the locally generated frequency in such a manner, that a very high intermediate frequency is resulting or by using piezo-crystal devices with enlarged width of band.

The selectivity of a circuit and therefore the passing width of a frequency band can be defined by the so-called half-value width. The half-value width of a resonance curve is the difference between the two frequencies on both sides of the resonance frequency, for which the amplitudes are equal and have the half-value of the resonance amplitude.

In order to prevent that the side bands of the intermediate frequency bands will be cut off in 5 a disturbing degree, according to the invention,

the band-width of the modulated intermediate frequency shall be smaller than the half-value width of the piezo-circuit.

The natural damping decrement of the piezo- 50 crystal may be =d, the highest modulation frequency may be :Af and the intermediate frequency may be :fo. According to the invention 2A1 must be smaller than djo. By this extreme relation the intermediate frequency o may then The invention will be more concisely described in conjunction with the accompanying drawing, of which 15 Fig. 1 shows the receiving device with a piezoelectric selection circuit and Fig. 2 shows an alternative form of transformer coupling for the selection circuit of Fig. 1.

In Fig. 1 there is shown an aerial circuit I with resistance members 2, 3 (each approximately 500 ohms) which is connected with the primary coil 4 of a high frequency transformer, the secondary coil 5 of which being connected with a variable condenser t. The primary winding 4 is adapted to an optimal extent to the practically constant resistance 3. The input circuit 5, 6 is tuned to the frequency of the incoming waves and effects the preliminary selection of the received waves for example between 200 to 2000 meters. The input circuit is connected with the one control-grid of the twin-grid mixing tube 7. An oscillating circuit, consisting of a variable capacity 8 and a coil 9, is connected withthe anode and over a blocking condenser with the other control-grid of the mixing tube. 1. The mid-point of the coil 9 is connected over the primary winding 30 of a transformer 50, H with the anode-current source. By means of the oscillatory circuit 8, 9 there are locally generated oscillations, which will be mixed with the incoming waves and therefore producing two intermediate frequencies being the sum and the difference of the frequencies of the locally generated waves and the received waves. By means of the following piezo-electric circuit ll, l2, l3, l4, l5 and 21 the sum-frequency I0 is selected according to the infradyne principle. Therefore, the natural frequency of the piezo-crystal w I2 and the whole piezo-electric circuit is tuned to the sum-frequency in.

The circuit 8, 9 is tuned in such manner that the intermediate frequency arising in the anode circuit of the tube 1 by reason of the infradyne effect which shall be the sum of the incoming carrier frequency and the oscillatory frequency generated by circuit 8, 9 and the inherent capacities of the tube, has a frequency value equal to the frequency 10 calculated from the above cited formula. V

By means of a transformer H), II the secondary side of which with the associated inherent capacities of the circuit is preferably tuned such as to resonate near the carrier frequency aris- 7 ing in the anode circuit of tube 1, this frequency is transmitted to a piezo-electric circuit in bridge connection according to the invention, the object of which is to reduce in respect of all frequencies outside of the natural frequency of the piezo-crystal and tuned to the intermediate frequency the throughgoing amplitude down to 1/100000 of the input value, but to allow the amplitude in respect of the resonance frequency to pass through as far as possible without attenuation. The piiszo-crystal I2, which. outside of its resonance is represented electrically by the capacity of its mounting, is supplemented by the condensers I3, I4 and I5 to form a; capacity bridge, whereby the coil I I is not earthed at any point, so that the earth potential depends on the impedance of I2 and,l3. The condenser I3 is preferably constituted by a differential con-' denser earthed with one pole. On this it is possible to perform subsequent adjustment from the outside. Static charges are conducted away over a resistance 21 of approximately ohms. The entire structure is situated within a screening means I6, which performs proper screening on all sides and also extends to the lead I1 to the grid of the next tube I8, and preferably may be supplemented by a total box screen for the entire after-connected receiver. According to the invention, the connected earth capacity of the line I! consists of less than of the part capacities I4, I5. The bridge is now adjusted in such fashion that all four capacities are ap proximately equal. The line I! must accordingly be short, and the grid capacity of I8 and also the capacity against the screening line small. If desired, the same may also be limited by a small condenser 28 of approximately 5 cm. The coils I0 and II should preferably act on each other only by induction, and the earth capacities of the poles of the coil II should be affected as little as possible by measures in the primary circuit of the coil I0. This object is approached according to the invention either by an electrostatic screening means 26 provided between the coils, or by an arrangement of the coils I0 and II in the manner illustrated in Fig. 2, whereby the parts of the winding of the primary coil I0 situated next to the coil II are connected with earth, and the coil I0 is preferably divided into two halves disposed symmetrically to I I. In this manner maintenance of the earth point as potential middle point of the secondary potential is facilitated.

The selection curve effected by the piezo-electric bridge-circuit shown in Fig. 1 using a completely flat ground piezo-crystal is equivalent to the selection of a single low-loss circuit. If the selection curve possesses too sharp a point with steep flanks there is effected a suppression of thesid'es of the frequency-band. In this case according to the invention for the sake of 'improved tone-colour there is obtained a widened resonance curve, by arranging side by side in a mounting I2 two crystals, the natural oscillafilter with particularly form coupling in the following intermediate-frequency portion of the after-connected receiver (20, 2I).

- Behind the piezo-electric circuit I8 the transmitted oscillations are preferably transformed by heterodyne effect in a mixing tube to an oscillation of lower frequency, (long wave) by which a more effective amplification will be attained than in case of higher frequencies. For this purpose it is possible in itself, in accordance with the patent application Ser. No. 751,189 of the 2d November, 1934, to employ the oscillation wave of the tube 1 or a wave harmonic thereto. 'More practical, however, is the use of a second mixing tube I8 oscillating to a fixed wave by means of the oscillating circuit 22, 23. In the anode'circuit of the tube I8 there is then produced an always constant and longer intermediate wave as a difference frequency according to the superheterodyne principle. The oscillatory circuit attention. The intermediate-frequency band filter coupling 20, 2I may be employed for amplifying the high tones, whilst 24 represents a simple receiver comprising rectifier and low-fre- 22, 23 of this tube, therefore, no longer requires quency amplifier or the like, which rectifies and reproduces the intermediate frequency wave. The grid leak resistance 25' of the tube I8 may thus be replaced with particular advantage according to the invention by a short-Wave choke, in which manner the penetration of long-wave interferences into the tube I8 is prevented.

I claim:

1. In a radio receiving system having an antenna circuit, an oscillator-modulator including an electron discharge tube having a tunable input circuit coupled to said antenna circuit and an oscillation circuit tunable to' a predetermined very high frequency whereby to set up oscillations in said tube of such a frequency that when heterodyned with the incoming signal-modulated oscillations the sum and difference fre-,

quencies are derived, an output circuit coupled to said oscillation circuit and comprising a selection circuit and a piezo-electric crystal tuned to the derived sum frequency, the constants of the oscillator-modulator circuits having such values and the sum frequency being so high relative to its modulation frequencies that the latter" are accommodated within the half value width of the resonance curve of said piezo-electric crystal.

2. In a radio receiving system having an-antenna circuit, an oscillator-modulator including an electron discharge tube having a tunable input circuit coupled to said antenna circuit and an oscillation circuit tunable to a predetermined very high frequency whereby to set up oscilla-- oscillation circuit and comprising a selection cir.

cuit and a piezo-electric crystal tuned to the derived sum frequency, the constants of the oscillator-modulator circuits having such values and the sum frequency being so high relative to its modulation frequencies that the latter are accommodated within the half value width of the resonance curve of said piezo-electric crystal, said output circuit comprising a coupling transformer, having a primary and a secondary coil, the primary of which is connected in the anode circuit of said tube, the secondary of which is connected in series With twocapacities, a differential condenser connected in parallel to said secondary coil, the rotary plate of said differential condenser being earthed and connected to one electrode of said piezo-crystal, the other electrode of which being connected with one terminal of said input coil.

3. In a radio receiving system having an antenna circuit, an oscillator-modulator including an electron discharge tube having a tunable input circuit coupled to said antenna circuit and an oscillation circuit tunable to a predetermined very high frequency whereby to set up oscillations in said tube of such a frequency that when heterodyned with the incoming signal-modulated oscillations the sum and difference frequencies are derived, an output circuit coupled to said oscillation circuit and comprising a selection circuit and a piezo-electric crystal tuned to the derived sum frequency, the constants of the oscillatormodulator circuits having such values and the sum frequency being so high relative to its modulation frequencies that the latter are accommodated within the half value width of the resonance curve of said piezo-electric crystal, said output circuit comprising a coupling transformer, having a primary and a secondary coil, the primary of which is connected in the anode circuit of said tube, the secondary of which is connected in series with two capacities, a differential condenser connected in parallel to said secondary coil, the rotary plate of said differential condenser being earthed and connected to one electrode of said piezo-crystal, the other electrode of which being connected with one terminal of said input coil, the junction point of said two capacities is connected by means of a condenser to the input circuit of a succeeding amplifier stage.

4. In a radio receiving system having an antenna circuit, an oscillator-modulator including an electron discharge tube having a tunable input circuit coupled to said antenna circuit and an oscillation circuit tunable to a predetermined very high frequency whereby to set up oscillations in said tube of such a frequency that when heterodyned with the incoming signal-modulated oscillations the sum and difference frequencies are derived, an output circuit coupled to said oscillation circuit and comprising a selection circuit and a piezo-electric crystal tuned to the derived sum frequency, the constants of the oscillator-modulator circuits having such values and the sum frequency being so high relative to its modulation frequencies that the latter are accommodated within the half value width of the resonance curve of said piezo-electric crystal, said output circuit comprising a coupling transformer,

having a primary and a secondary coil, the primary of which is connected in the anode circuit of said tube, the secondary of which is connected in series with two capacities, a differential condenser connected in parallel to said secondary coil, the rotary plate of said differential condenser being earthed and connected to one electrode of said piezo-crystal, said electron discharge tube having a cathode, an anode, two control grids and a screen-grid, the first control grid being connected with said input circuit, the second control grid and the anode being connected with said oscillation circuit, a centered tapping point at the coil of said oscillation circuit being connected with an anode current source via said primary of the coupling transformer consisting of two parts arranged on both sides of the secondary coil connected to the.mid-point of said two coil-parts of the primary being earthed.

5. In a radio receiving system having an antenna circuit, an oscillator-modulator including an electron discharge tube having a tunable input circuit coupled to said antenna circuit and an oscillation circuit tunable to a predetermined very high frequency whereby to set up oscillations in said tube of such a frequency that when heterodyned with the incoming signal-modulated oscillations the sum and difference frequencies are derived, an output circuit coupled to: said oscillation circuit and comprising a selection circuit and a piezo-electric crystal tuned to the derived sum frequency, the constants of the oscillator-modulator circuits having such values and the sum frequency being so high relative to its modulation frequencies that the latter are accommodated within the half value width of the resonance curve of said piezo-electric crystal, said output circuit comprising a coupling transformer, having a primary and a secondary coil, the primary of which is connected in the anode circuit of said tube, the secondary of which is connected in series with two capacities, a differential condenser connected in parallel to said secondary coil, the rotary plate of said differential condenser being earthed and connected to one electrode of said piezo-crystal, the other electrode of which being connected with one terminal of said input coil, the junction point of said two capacities is connected by means of a condenser to the input circuit of a succeeding amplifier stage, said succeeding amplifier stage containing an electronic valve with a cathode, an anode, two,

control grids and a secreen-grid, the first control-grid coupled with said piezo-electric circuit, the second control-grid and the anode connected via a coupling circuit to an oscillatory circuit for locally generating oscillations mixed with the intermediate frequency and therefore changing the intermediate frequency to a constant longer intermediate wave, said latter coupling circuit containing a band filter for amplifying the high tones.

6. An arrangement according to claim 1 in which said piezo-electric crystal consists of two crystals with natural frequencies differing by approximately 5000 periods mounted side by side between two electrodes.

KURT SCHLESINGER. 

